This invention relates to systems for the purification and recovery of industrial solvents, such as solvents used in dry cleaning or textile treating processes. More particularly, the invention concerns filtration of a contaminated solvent, and a device for rinsing or cleansing the filter element.
Recent emphasis on the environmental hazards of industrial solvents has led to the development of systems for the recovery and reuse of the solvents. In the laundry and dry cleaning industry industrial solvents, such as perchlorethylene, are used. The perchlorethylene is frequently augmented with surface active chemicals, or surfactants, to enhance the textile cleaning capability.
In a typical dry cleaning facility, the solvent solution is fed into a dry cleaning tumbler during the cleaning cycle. After the dry cleaning cycle is complete, contaminated solvent fluid is discharged from the tumbler for recovery or recycling. The contaminated solvent fluid contains dirt, lint, and other residue or debris, as well as any surfactants and other non-biodegradable chemicals. In the prior art, replaceable filter cartridges, composed of pleated paper and a carbon core, have been used to filter the contaminated dry cleaning solvent. One difficulty with the replaceable cartridge is that the paper and carbon become saturated with hazardous waste that must ultimately be disposed of in compliance with environmental regulations.
More recently, the replaceable filter cartridge has been replaced by the more efficient distillation process for recycling contaminated perchlorethylene solvent. Reclamation by distillation is preferable over other techniques because it reduces the amount of hazardous waste generated by the process that must ultimately be disposed of in accordance with environmental regulations.
One drawback of the distillation technique is that it is relatively inconvenient and expensive to do in a continuous batch mode. Consequently, in many dry cleaning solvent reclamation systems, only a small percentage of the solvent within the system is passed through the distillation process.
Because the distillation apparatus eliminates the need for the replaceable carbon core filter cartridges, a chemical filter is no longer required. However, since the solvent fluid is not continuously distilled, filters are used to eliminate residue or debris from the contaminated solvent fluid. In one such apparatus, a stainless steel filter element is situated in a recovery loop to capture the debris suspended in the contaminated dry cleaning solvent fluid. Through continued use, the filter element becomes encased in the debris so that back pressure in the filter increases and the amount of dry cleaning solvent being recycled is reduced. In order to prevent this reduction in solvent flow, the filter element in prior art devices is cleaned using a backwash technique in which fluid is flowed through the filter in a direction opposite to the normal filtering direction. The debris is dislodged from the surface of the filter and collected for later disposal.
Backwashing techniques generally require a high volume of fluid in order to completely clean the filter element. Moreover, backwashing has a tendency to collapse cylindrical filters, unless a stiffer, more expensive, filter element is used that will not collapse under the moderate backwashing pressures. There is a need, particularly in the field of dry cleaning solvent recovery, for a filter rinsing or cleansing device that utilizes a low volume of fluid to completely rinse the filter element of adhered residue, without the risk of collapsing the filter element during the rinsing cycle.